1. Field of the Invention
The present invention relates to shock absorbers for vehicles. More particularly, the disclosure relates to fluid dampers. More particularly still, the disclosure relates to methods and apparatus for controlling and managing dampening through the selective use of dampening fluid having variable flow characteristics.
2. Description of Related Art
Magneto rheological fluid (MR fluid) is a variable character fluid comprising a (e.g. colloid like) suspension of micrometer-sized particles in a carrier fluid, often a type of oil. When subjected to a magnetic field, the fluid greatly increases its apparent viscosity and/or shear strength. The particles, which are typically micrometer or nanometer scale spheres or ellipsoids, are active when subjected to a magnetic field (e.g. such as iron particles) and are distributed randomly and in suspension within the carrier liquid under normal circumstances. When a magnetic field is applied to the liquid suspension, however, the particles (usually in the 0.1-10 μm range) align themselves along lines of magnetic flux. When the fluid is contained between two poles (typically of separation 0.5-2 mm), the resulting chains of particles restrict the movement of the fluid, perpendicular to the direction of flux, effectively increasing its viscosity and/or shear strength. The yield stress of the fluid when it is “activated” or in an “on” magnetized state can be controlled very accurately and quickly (typically a few milliseconds) by varying the magnetic field intensity.
There are problems arising from the use of variable viscosity fluids, like MR fluid in mechanical applications. For example, even in the absence of electromagnetic energy, MR fluid is very dense, resulting in much greater viscosity and strength (up to four times) compared to “normal” fluids. Mechanical systems using such fluids may not be capable of handling corresponding dynamic loads.
Another problem with the MR fluid is its abrasiveness. This abrasiveness is caused by the ferrous particles suspended in the oil as they can have a sandpaper effect on all of the moving parts. Mechanical systems employing such fluids may be rapidly worn out.
What is needed is a damper for a suspension system that utilizes variable rheology fluid in a manner that avoids problems associated with use of such fluid.